1. Field of the Invention
The present invention relates to a device for controlling a fuel feed pump used for an engine.
2. Description of the Related Art
In a known fuel feed pump control device for an engine, a fuel spill passage is branched from the high pressure fuel passage connected to the discharge port of the fuel feed pump driven by the engine, and a spill control valve is arranged in the fuel spill passage. The fuel feed pump control device is provided with a pressure chamber, and the pressure therein is controlled by the piezoelectric element. The spill control valve is controlled by changing the pressure of the working liquid contained in the pressure chamber (see Japanese Unexamined Utility Model publication No. 63-138438).
In this fuel feed pump control device when the piezoelectric element is expanded, and accordingly the pressure of the working liquid in the pressure chamber increased, the spill control valve is moved by the pressurized working liquid and closed. Conversely, if the piezoelectric element is contracted, and accordingly the pressure of the working liquid in the pressure chamber is lowered, the spill control valve is opened and a part of the pressurized fuel in the high pressure fuel passage is spilled out. Consequently, in this fuel feed pump control device, by controlling the spill control valve with the piezoelectric element, the amount of pressurized fuel discharged from the high pressure fuel passage connected to the discharge port of the fuel feed pump is controlled, and the amount of this pressurized fuel discharged as mentioned above is increased as the closing time of the spill control valve becomes longer than the opening time thereof.
In this fuel feed pump control device, when the piezoelectric element is expanded, and accordingly the pressure of the working liquid in the pressure chamber is increased as mentioned above, a part of the pressurized working liquid leaks from the pressure chamber. Nevertheless, even if a part of the pressurized working liquid leaks as mentioned above, when the piezoelectric element is contracted, and accordingly, the pressure of the working liquid in the pressure chamber is lowered, fresh working liquid is fed into the pressure chamber via the check valve to make up the loss of the working liquid. Consequently, when the piezoelectric element is again expanded, the pressure of the working liquid in the pressure chamber usually can be increased to a predetermined pressure.
In such a fuel feed pump control device for controlling the fuel feed pump driven by the engine, however, the piezoelectric element is expanded at a predetermined crankangle of the engine, and the piezoelectric element is contracted before it is again expanded. Consequently, when the engine is operating at a low speed, if a degree of the crankangle during which the piezoelectric element remains expanded becomes larger than a degree of angle of the crankshaft rotation during which the piezoelectric element remains contracted, the time during which the piezoelectric element remains expanded becomes very long, and as a result, since the pressure of the working liquid in the pressure chamber during this time becomes much lower due to the leakage of the working liquid, a problem occurs in that it is impossible to maintain the spill control valve at the closed position.